Protection of bore surfaces of guns



.March 29, 1949.

H.B. ALLEN ETAL PROTECTION OF BORE SURFACES OF GUNS Filed April 28, 1945l 2 Sheets-Sheetl l kll` Nital H Emth MMMMMWM@ www 2 Sheets-Sheet 2 H.B. ALLEN I'AL PROTECTION OF BORE SURFACES OF GUNS March 29, 1949 FiledApril 28, 1945 Patented Mar. 29, 1949 2,465,962 PROTECTION OF BORESURFACES OF GUNS Henry B. Allen and Pa., assignors to Nicol H. Smith,the United States of America Philadelphia,

as represented by the Secretary of War Application April 28, 1945,Serial No. 590,846

6 Claims.

The invention relates to means for protecting and prolonging the life ofthe throat and rifling in ordnance pieces, and seeks particularly topresent means especially applicable to use in current gun models withlittle modification. It is well understood that erosion at the forcingcone and adjacent riing by the highly heated and rapidly moving gases atthe high pressures involved in the gun chamber, and the diversion andcompression thereof in the throat marks the beginning of deteriorationof bore faces and riling. This is soon followed by a condition whereonfiring shock and shearing effects occur by the projectile moving withoutrotation from the chamber over a part of the bore where riiiing has beendestroyed, and then encountering partly eroded rifling afterconsiderable acceleration. This may then become the major factor indeterioration of the bore.

An object of our invention is the provision of an effective andthoroughly reliable method for protecting the bore surfaces of guns frominfluences of a wide variety which otherwise lead to erosion anduntimely wearing out of the gun.

A further object of our invention is the provision of mechanicallysimple and inexpensive means for protecting the bore surface of a gunfrom wear and deterioration by propellant explosives, which may beincluded in the ammunition as loaded into the gun incidental to simplefiring routine.

A principal aim of the invention is to provide an expendible inexpensivefacing or chambering element in the round itself which will afford asurface material suicient to withstand the erosion manifest in firingthe single round at least, this material extending over only thecritical area where erosion has heretofore been observed to start inconventional bores, so that the further deterioration by shock and shearafter initial erosion will be avoided, as Well as erosion otherwisematerially reduced.

A still further object of our invention is the provision of a gun whichis adapted to receive chambering rounds of ammunition including boresurface protective means.

Other objects of the invention will be obvious, and in part pointed outhereinafter.

The invention accordingly consists in the individual elements,combination of parts, composition of materials, and in the severalsteps, and the relation of each of the same to one or more of the othersas described herein, taken in the light of the accompanying drawings:and set forth in the following claims.

In the drawings herewith Fig. 1 is a longitudinal sectional view of around of ammunition embodying certain features of our invention;

Figure 2 is a detail elevation of the sleeve;

Figure 3 is a fragmentary section of a round showing the standard .50caliber bullet and a short sleeve;

Figure 4 is a fragmentary longitudinal section of a gun barrel, moreparticularly of chamber and bore portions;

Figure 5 is a longitudinal section of the barrel and round illustratedin Figures 1 and 4, the representations of land forms being purelyformal;

Figure 6 is a similar View showing the use of a short liner sleeve withmodification of the barrel;

Figure 7 is a similar view showing the invention adapted to the currentball ammunition.

As conducive to a clearer understanding of certain features of ourinvention it may be noted at this point that gun erosion is a complexphenomenon involving a combination of numerous effects; predominantlythermal effects, chemical and metallurgical effects, and mechanicaleffects. all of which contribute, as the result of gun use, toshortening the useful life of the gun. The individual or combinedintensity of the various effects is dependent upon such factors as gunmaterial, type and quantity of powder and type of projectile employed,rate of fire, and velocity of projectile. Gun erosion is most severewithin an area beginning at the forcing cone and origin of rifling andextending some few calibers along the gun barrel toward the muzzle.

As the result of high temperatures reached by the powder gases, a thinlayer of metal at and near the bore surface of the gun is rapidly heatedto a temperature which, under certain circumstances, exceeds meltingrange of the metal. Even if the bore surface is not melted, thetemperatures reached are such as to reduce the strength of the steel andfacilitate its displacement. In cases where gas leakage occurs thematerial may be simultaneously melted and carried away to a markeddegree by scouring action of the escaping gas.

At the high temperatures attained by the powder gases the products ofpowder explosion are chemically active. Furthermore, the raising of thebore surface temperature increases the chemical reactivity of the gunmaterial. As a result, there is a very complex set of reactions betweenthe gun material and the powder gases. The importance of chemistry inthe erosion process has not as yet been fully evaluated, but theexistence of a considerable variety of reaction products has beenestablished.

the beta allotropes are exceeded. This layer has... lower strength,probably a lower melting ,e point.

due to chemical effects, and seemingly is less resistant to erosion thanthe underlying steel.`

There are several mechanical eifects which are known to contribute tothe erosion process. In

the first place, simple frictional or yabrasive wear by contact of theprojectile is a factor, the importance of which depends upon gun andprojectile design and materials. When the steel surface of a projectileYbears upon a bore surface of steel, galling may occur in addition toabrasive wear, with consequent removal of small masses of metal from thebore surface. Both the abrasive wear and galling tendency are aected bythe surface temperatures attained in the bore. The temperature at thepoint of rubbing is influenced by the instantaneous heating effectcaused by friction.

It is also to be noted that in conventional guns bore diameter isincreased at the bore surface as a result of intense surface stressesdeveloped by engraving. This is particularly `true under rapid reconditions, when the gun is quite hot. Metal in the lands is displacedradially outward, forward, and circumferentially sideways. Even thoughno metal is actually removed, the lands are gradually obliterated, bybeingchammered, swaged or pressed down into the surface from which theyat rst rose and by being broadened and extended by attening. Anydownward radial ldisplacement of that portion of a land under theprojectile rotating band is accompanied by an upward displacement of theland surface ahead of it. In effect awave, consisting of a depression ofthe land material near the origin of riiling and a raising of materialin front of this point proceeds down the bore as ring progresses.

An outstanding object of our invention, accordingly, is the provision ofa method forL conditioning gunsso as to improve gun resistance toplastic deformation and toerosion normally producedl by thermal,chemical, metallurgical, and mechanical effectscombined orseparatelyincident to firing of conventional ammunition.

Referring now more particularly to the practice of our invention, weincrease the useful life of any of acwide variety of smooth bore orrifled guns of different sizes to be employed for automatic or singleshot fire at high or low velocity, through the use of thin sleeves whichprovide a protective covering for the bore surface of the gun over atleast that part where most severe erosion and deformation commonlyoccur. The sleeves preferably are affixed as individual elements to thecases of fixed ammunition to be red in the gun, or-illustratively--mayconstitute vintegral extended portions of such cases, so as in eitherevent to be insertable or ejectable with the case in the normal firingfunction of the gun.

In order to make sleeve protection of the bore surfacespracticable atthe breech end oi the bore we prefer Ato-provide a gun which has aslightly enlarged bore including the forcing cone .toward the muzzleYand extending for a distance suiicient to permit and ensureproperchamber,-

ing of the ammunition including the sleeve. Aside from the feature justmentioned, the gun barrels conveniently are wholly of conventionalcontour along the bore surface. Preferably, but not essentially, thebore surface, illustratively at least that part immediately in advanceof the enlarged bore portion and continuing forward to the muzzle, is ofchromium or other erosion-resistant material.

In Figure 1 of the accompanying drawing there is represented at l0 anillustrative round of case ammunition which we employ in the practiceoi' our invention. The particular round shown corresponds Ato one ofartillery type used by us in a Y.50 caliber ried gun, although theinvention may usual ,primer centered lin the base thereof. 'ThenAforward. part of the Vcase comprises a tapered shoulder iportionlZ whichterminatesy in a conventionalopen neck `I 3.A An artillery typeprojectile or; bullet I4 (of approximately 0.5 inch diam-` eter)v fitsrmly into theopen'neck and has an interposed rotating band I5 setwithin-and eX,-

tendingforwardlyof the outer edge of the neck..

Al thin sleeve I6, illustratively madeA of drawn. soft steeltubing andhaving a `wall thickness of about 0.010 inch, is mounted over the caseneck..

vIt is :formed witha large diameterrear part l1,

and tapers down before-but. not necessarily enr., gavging-the projectilerotating band .as at I3.,

so asv to provide kforwardly ar slightly reduced cylindricalforward partI9 having an inner diam.- eterwhichis slightly more than 0.500 inch. On

this .di'ameter'the sleeve `extends from near the rotating bandiorwardlyover the surface of the projectile to .a distance somewhat in advancevof.

the projectile nose in this particular form. The

sleevefforthe,` sake of simplicity ofY assembling, preferably is madevso as to be slipped readily into this position onthe round aftermanufacture of the standard prior round... In order to ensureproper'withdrawalfof thesleeve when the car- .tridge is extracted bybreech mechanism after the round has been flreduwe provideseveralperipherally spacediindentations orperforationsl in the sleevenearthe Abase of the same prefer:

ably located so as to be rearwardly ofr theY bullet g asin Fig, 1'. Theholes may ,be circular, orrectangularas inFigrZ, to afford better keyingwith the cartridge. When, the. round Vis ined, metal `of.

the case neck is forced permanentlyinto the per: forations by powder gaspressure within thecase,

to effect apositivelock betweenthe case and the sleeve.

For Vfiring the ammunition, We provide a gun havinga ried barrel 2|:(see Fig. el of the drawing) which is modiedadjacent the` chamber to.vaccommodate the sleeve element. I 6.; 4The `forward part or neck2'lofthe chambentheforcing cone 24 and adjacent relievedsectioni 22 .of theried bore,are enlargedzn radius as `compared with conventionalfguns byan amountI whichV is substantially equal tothe. thickness'fo'f thesleeve- It 4'will be noted that .the rifling'zaextends from the lfore@-ing -cone A2l! Aforwardalongthefbore surfacev tof the enlarged bore.section22, v.then is stepped or;

inclined inward at 25 and continued conventionallythrkough the`advancedportion. 2,6 'lof the bore,

s which may be of conventional caliber and length.

With a round of sleeved ammunition properly chambered in the modifiedgun, as illustrated in Fig. of the drawing, the bullet rotating band I5is disposed immediately in back of the forcing cone :24. The forcingcone and rifled bore surface extending therefrom are separated from thebullet by sleeve I6 which rests on or is substantially geometricallycongrous with the bore surface, including the forcing cone and land tops28 of the enlarged bore section. At its advanced end the sleeve adjoinsthe .50 caliber section of the rifiecl bore and is substantially alined,inside, with the land tops of the same.

When the gun is fired, using the round of Fig. l, the bullet I4 carriesrotating band I 5 past forcing cone 24, at which time engraving of theband by means of the rifling begins through sleeve I6. The sleeve alsois actually engraved by extrusion into the grooves along with therotating band. Before and during this period metal of the shell case IIis forced by powder gas pressure into the perforations 20 at the base ofthe sleeve for locking or keying the two elements together. The sleeveprotects the underlying metal of the gun from erosive effects of the hotpowder gases as well as from mechanical effects set up at the forcingcone and by subsequent engraving: also by insulation of heat from thetube material. After the bullet reaches the end of the sleeve,additional engraving of the band or bullet case which may be necessarytakes place in the advanced bore section. After firing, the hot case andhot sleeve attached or keyed thereto are ejected from the gun by theusual breech mechanism operating on the case (removing a substantialamount of heat which was prevented from reaching the barrel), followedby loading, firing and ejection of successive similar sleeved rounds asdesired. The overall effect is to relieve the gun bore surface ofexposure to the most severe conditions which normally contribute toerosion and plastic deformation, with the result that useful life of thegun is considerably increased.

While it is desirable to extend the protection of the forcing cone 24and rifling in the bore as far toward the muzzle as practicable there isa limit to the practicability of extension of the sleeve and also apoint of economic balance and compensation between the benefit ofprolongation of life of the weapon by this method and cost of modifiedammunition and gun, modification of handling routine, and modificationof belts and firing mechanism. The sleeve of Fig. l has been foundpracticable` but in order to limit expenditure of material and for otherreasons it has also been found very beneficial to use a sleeve whichdoes not extend beyond the bourrelet or possibly the beginning of theogive. This is especially satisfactory when the bore forwardly of thesleeve I6 (or I6 hereinafter described) is faced with a wear resistingmaterial. There is a peculiar coordination of these two featurespracticable which is distinguished from merely facing the gun surfaceswith wear resistant material. Thus, the hard materials available andsuitable for the use are scarce and expensive; they can only bepracticably applied in thin facings; facings which are effective toassure an adequate length of service to bore faces at a distance fromthe conventional chamber are incapable of preventing deformation ofunderlying material of the gun tube at the forcing cone, due to hightemperatures effective through an otherwise adequate facing, and wouldpermit plasticising and deformation of such underlying material. Butwith the use of the short sleeve (Fig. 3) and its repeated renewal oneach round, the lowering of temperature of the gun tube material byabsorption and impedance in the sleeve and by conduction to the freshsleeves; a moderate degree of insulation, and the dissipation of heat bythe removed sleeves; as well as protection of the overlying material ofthe gun tube against erosion, enable a very extended use of the gun withimmaterial depreciation of the forcing cone and adjacent rifling, andpractically no wear of the forward riing, when the thin facing is usedfrom the chamber forward.

In Figure 3, the sleeve and parts corresponding to those alreadydescribed in the sleeve I6, have the same reference characters with theaddition of a prime mark. The cartridge case is unchanged, and the rearlarger part I 'I' of the sleeve is of the same thickness, diameter andlength as the part I1; the taper I8 is the same as the part I8 of sleeveI6, but the forward reduced part I9' of this sleeve, while of the samethickness and diameter as in the forward part of the sleeve I6, is onlyabout one halfor less than half-the length of the forward part I 9 ofthe first described sleeve. This figure also illustrates a conventionalsoft jacket standard boat-tail bullet I4', familiar in the type of armindicated. Its jacket 29 serves in place of the rotating band I5, and isengraved by the rifling of the barrel, with the same effect.

Although marked increase in gun life is obtained without shielding thatsection 26 of the bore surface beyond the protective sleeve I6', weprefer to face this section, including land and groove surfaces, witherosion resistant and corrosion resistant material such as chromium, orother material, as, molybdenum, tungsten or tantalum, in normal orhardened condition. The

advanced facing thus constituted, preferably, andy 4for best results,may be electro-deposited or otherwise formed to such thickness as willprevent the formation of heat-transformed layers in the underlying gunmetal. By using the advanced facing, the length of sleeve on the caseammunition may be shortened as compared with the length desirable whenthe lining is omitted. It will be understood, however, that theshortening of the protective sleeve is not essential, and also that ashortened sleeve may be used without necessarily facing any parts of thegun bore with harder metal.

Dlustrative of that embodiment of our invention which includes theadvanced lining or facing, a gun barrel 30 riiled from adjacent theforcing cone 3| to the muzzle is shown in part in Fig. 6 of the drawing(the muzzle being omitted). It has a thin, adherent, electrolytricallydeposited chromium plate or facing 32 on the bore surfaces, extendingcontinuously from the shoulder 34 of the chamber and across the forcingcone 3I beneath and adjacent the part I9 of the protective sleeve I 6'of the cartridge case I I, and covering the advanced bore surface 26 upthe barrel for a substantial distance, or all the way to the muzzle (notshown). A thickness of chromium plate ranging from 0.003 inch to 0.006inch or more preferably is used as the facing 32 to prevent heattransformation or other objectionable modication of the underlying steelat least in the barrel beyond the sleeve IS; and in such thickness thechromium of the thickness named, in automatic arms of considerable rangeof caliber, and specifically the .50 caliber Browning machine gun isfound to remain intact over an exceptionally long period of use. Y

In this-ligure ,(6) the snortsleeve; l this shownff as in Fig. 3. Thechromium plate 32 in the ad, vanced bore section, deposited over therifled steel, provides the standard caliber finished rifled boresurface.-

While the whole bore of the barrel, 30 upon which the facing 32, is tobe applied must be tooled to, a larger than standard radius for agivencali'.- I

must'be also an allowance for the thickness .of the.

sleeve inthe width of the lands in the part 35. Thus, if the lands intheadvanced bore 26 are to have a given width of finished land face v36,

the lands 31 as tooled vin that partv should bev approximately 0.006pinch narrower wherethe facing y32 'is tobe 0.003 inch thick. In the enlarged bore 35, however the tooled lands 38 should be approximately0.026 inch narrower, where the rotating ring is to require no ,materialfurther engraving afterleaving the sleeve. If it is desiredthat thereshall be some small degree of further engraving performed ,by the bandsof the forward bore 26' the lands 38 may be reduced in height, thatY is,their radius increased somewhat x furtherthan the 0.013allowancelnecessary for they sleeve and facing aloneand the reduction ofwidthA of the tooledlandsu38 may be, say 0.027,-V

necessary. In such case also, .while the sleeve I6 is not shaped torifle form on firing, as in the previously described gun, it willprotect. thehoreH from the severest erosion, corrosion, and plas.-ticising effects heretofore incident to rapid fire of the gun, so thatthe advanced bore lands 43 will be subjectto less deterioration. And ifthe advanced bore d3 and relief 42 are faced as indicated at 45, itslife is extended many times that of the conventional barrel in suchguns.

Usingthe round of Fig. 6, the round is. cham-1 bered in the barrel sothat the rotating'band v is directly behind the forcing cone 3l, withthe sleeve I6' taperingat I8' with the forcrig'cone,

to the smaller diameter i9 over plated rifling of the relieved boresection 22'.

When a gun comprising barrel 30 of Fig. 6, with chambering: caseammunition of the :character there shown, is fired, the artillery typebullet I4 carriesrotating band I5 past forcing cone 3 I, and

' engraving of the rotating band by the lands of instead,;ofp0.026.Theallowance of- 0.026 inch,A

would result inthe interior surfaces of the sleeve part I9 being-shapedby the band I5 to thesame f contourand measurements as ,theinterioriinished faces of the riingofthe advancedborel 26. The-greaterallowancementioned (0.027 inch) will insure that the material of thesleeve pressed# into the riing of the relieved lpart will havean innercross section surface form'the same as that. of the, advanced bore,'butYdiffering lsufficiently in dimension at Ithe inner faces of the sleevelto re-l quirea lslight additional engraving of Athe band I5 as thelandsof the advanced part of the barrel y are4 encountered. Thisconstruction, requiring relief of the neck for the facing 32 inadditionto the allowance for the sleeve, results, in r,shortening the shoulders34 of the chamber as tooled but still affording an adequate stop forengaging; the

shoulder I2 of the cartridge. The step 39 lne--l tween .the enlargedbore v35 and the advanced bore 26. may be sloped as before at4 25in Fig.4orV otherwise shaped as requirementsv dictate.

It isA believed that the iinishedsurfacesxof the relieved part 35'maybesuch that a close aline.- ment lof all internal surfaces of the sleeve(as formed when pressed ontoyand into'the rilng of the relieved part 35)with corresponding surfaces i of the advanced lbore 26',may beattained,vso that less, or-no further engraving of the band I5 will berequired after it clears the sleeve.,

Incase the boat-tail bullet is used,v the prior practice'inraising thelands gradually from a cylindrical unried bore as a1; 4I of barrel 40.

(Figf)` in advance .of the neck .of the chamber may be followed, as at44inFig. 7. Therelief 42 of the smooth bore for reception of our sleeveinsuch case would `terminate short ofthe beginning of the vlands 43,this beginning M lof the. lands being advanced forward1y.:..in`the-,bore 1f/s section22 acting through sleeve I6 ensues. The

sleeve is also shaped to the plated riling Iby pressureof the rotatingband, at the same time that rthe latter is engraved. When the bulletreaches the end'of the sleeve, additional engraving may take placedirectly onthe plated riiiing of the advanced bore section if there islack of registry purposed or accidental of the shaped sleeve andadvanced rifling. After firing, the case II, with lthe sleeve positivelyattached by the keying means 20 as; described is ejected from the gun,followed by loading, firing and ejection of similar sleeved rounds asdescribed. rhe over-all effect is to relieve the gun barrel includingforcing cone and riiied bore surface of exposure to the most severeconditions which normally contribute to erosion and plastic deformation,with the yresult that life of the gun is prolonged to a surprisingextent. 4The chromium plating protects the advanced bore section ,fromerosive effects and for itself is spared in large measure frommechanical effects set upk by they bullet. Actually, as the inventionhas been heretofore practiced, the bullet is largely or @Wholly engravedIbefore coming into direct contact with the plated bore surface.

The function as described is the same with either the long or shortsleeve and artillery type bullet. The function with the conventionalhall cartridge of Fig. 3 will be understood without detailing, thesleeve simply protecting the smooth bore from erosion and deformation aswill be understood, while the engraving of the bulletoccursconventionally on the faced lands 45.

The forcing cone and relieved surfaces for accommodating the forwardreduced end of the sleeve are not regarded as part of the chamber f ofthe gun, but the latter comprises only that enlarged part whichaccommodates the conventional `cartridge case and extending from thebreech face of the gun tube ordinarily, to the forward end cf the neckportion 2. The chamber includes the shoulder 3:3 which receivesthereagainst the shoulder I2 ofthe case II. The surfaces for- -wardly ofthe forcing cone are regarded as parts of thebore technically.so-called.

Results of numerous tests show that guns and ammunition provided andcombined in accordancewith our invention to a large extent reduce lgunerosion and plastic deformation. The ammunition sleeves shield thebreech bore surface from thermal, chemical and metallurgical, and

mechanical effects combined, and in ried guns o make it pcssiblewhenusing raised rotating band valnmlunition to bring substantiallypre-engraved bullets to the riing without any problem of orientation ofthe bullets in the barrel prior to firing. The erosion-resistant metalfacing or lining on the advanced bore surface contributes much to theuseful life of the guns, especially when provided in such thickness asto prevent heat alteration of the underlying steel and when affordedsleeve protection against initial stress and wear normally caused byengraving function and other forces.

In machine guns of the kind named herein there are recognized rates offire (as, for instance, 800 shots per minute or more) which rapidlybuild up heat in the barrels, and it was a prior practice to limit thelength of the bursts, and require intervals between bursts sufficient topermit dissipation of the heat transferred to the barrel. In watercooled guns this tendency to heat is reduced but not entirelyeliminated, and the interior faces will pass the critical temperatureunder sustained automatic fire. Air cooled guns Will be morepronouncedly heated. yIn large caliber guns the frequency of re may beof the order of thirty shots per minute, more or less, according to thecaliber, but due to the larger charges of propellant used, the barrelsstill accumulate heat and the allotropic form of the barrel materialchanges, as earlier stated herein. With our changeable sleeve, using anew one on each shot, there may be approximated a balance (betweentransfer of heat to the barrel, and its diusion in the barrel anddissipation by radiation, conduction and convection) in which a certainrate of re may be sustained indenitely, the sleeve shielding the barrelsufficiently, and its extraction removing heat before material transferto the barrel, so that progressive dissipation of heat from the barrelmay keep its mean temperature below a point of dangerous excess,especially adjacent the chamber in the part of the barrel ordinarilymost subject to erosion. This will permit either continuous automaticfire as long as ammunition is available, or will permit much longerbursts at very high rates of machine gun fire; or more frequent ring ofother types of guns.

Thus it will be seen that in the present invention guns and ammunitionare provided and combined so as to prolong useful gun life, and that theobjects hereinbefore noted together with many other thoroughly practicaladvantages are successfully achieved. The invention eliminates orminimizes many difiiculties encountered in repair and replacement oferoded guns and the associated problems of production andtransportation.

It will be understood that while the use of chromium facings such ascoatings, claddings, sleeves or plates covering the bore surface fromand in advance of the ammunition sleeve is preferred, the facings may bedispensed with entirely, or other erosion resistant metal, compositemetal, or alloy metal facings employed where practical.

It will be understood that it is within the scope of our invention tomodify conventional guns, as by machining or electropolishing the boresurface so as to make room for the ammunition sleeve with or without theadvanced protective facing, or to provide guns initially which aresuitable to receive the ammunition sleeve with or without the advancedlining or facing of the bore.

Since many possible embodiments of our invention may be made, and asmany changes may be made in the embodiments hereinbefore set 10 forth,it will be understood that the matter described herein is to beinterpreted as illustrative and not invariable.

We claim:

1. A round of ammunition comprising in combination a case body shaped tot the chamber of a gun barrel, said case body shaped to hold aprojectile, a projectile seated in said case body and projectingforwardly from the case body, said projectile having an enlarged partdeformable by a gun barrel when fired therethrough, conventional primerand propellant means in the case body, and a sleeve on the case bodyextending forwardly thereof around said projectile beyond the enlargeddeformable part, the sleeve shaped and proportioned to extendlongitudinally within the bore of a gun barrel in which the round isloaded and in advance of said deformable part of the projectile so a'sto lie over the bore area of principal erosive and corrosive tendencyand means on said sleeve for positively retaining same on said caseafter the round is fired.

2. A round of ammunition comprising a case for conventional chamberingin gun barrels, said case having an open forward end, a projectileseated in the forward end of said case and projecting therefrom, a thinsleeve in contact with said case and extending therefrom over at least apart of said projectile, and means for retaining said sleeve attached tosaid case after the round is red, said case being provided with aforwardly opening neck portion of reduced diameter and said projectilebeing of the banded artillery type and is seated partly within said neckportion and partly protruding therefrom, said projectile having arotating band of diameter greater than the neck of the case, and saidthin sleeve being of erosion resisting material and extending from saidneck snugly over said band and around the largest diameter ofr saidprojectile.

3. In combination a round of ammunition and a gun barrel, said roundcomprising a case, a projectile seated in the forward end thereof, and athin ductile, erosion resistant sleeve attached to and extendingforwardly from said case over at least part of said projectile, said gunbarrel comprising a rifled bore and a chamber for receiving said round,said chamber comprising a rified section corresponding to the sleeveportion of said round forwardly of said case, whereby said sleeve willbe shaped by said rifling when the round is fired.

4. The invention as recited in claim 3 wherein the rified section ofsaid chamber is enlarged to an extent equal to the thickness of saidsleeve, the riing of said enlarged bore being aligned with the rifiingof the advanced bore, the width of the lands of said rifling of theenlarged bore being reduced correspondingly, wherein the rotating bandof a projectile fired therein will be engraved on the inserted sleeve tomatch the riing of said advanced bore section.

5. A combined ammunition round and gun bore protecting device comprisinga conventional ammunition round proportioned to fit a gun barrel havinga conventional forcing cone, including a projectile and a sleeve oferosion resistant material fixed as a part of the round unit, saidsleeve having a reduced forward part .extending forward around theprojectile beyond the normal line of securement of the proiectile in theround and reduced so as to extend forwardly of the forcing cone of abarrel in which the round is inserted and to lie upon the bore surfaceof such barrel a substantial distance beyond the forcing -1rcone,' 'and4means on' said sleeve' for'positively "',r'etain'ing same .in a gunbarrel yafter the round Ais red, the projectile havingapartv of afcliaineter and material such as to tbe -engravable by rlfling of arified bore barrel in which the round 6.` A combine-idv ammunitionroundand gun bore irprote'ctingdevice comprising a conventional propellantcharge, primer and container, a projectile 'extended Vforwardlytherefrom and having an exf'posed part engravable by bore riding, and asleeve of'erosion yresistant material xed aspart of the round unit andhaving apart extended forwardly around the projectile beyond saidengravable-part 'so as to extend into 'the bore'of a barrel in whichthe'roundr is inserted and to lie upon the bore Asurface of suchbarrel'over a substantial distance beyond the chamber of such barrel and'cooper- Lating locking means on said sleeveand retainer lfor/retainingsaid sleeve looked to sadcontainer ,-.after :the round is V fired, saidmeans being operable'Y by gas'pressurey due to firing.

vHENRY B. ALLEN.

' NICOL I-L'SMITH.

e REFERENCES CITED The `following referencesv are of record in the le ofthis patent:

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